1. Field
The present invention relates to wireless communications. More particularly, the present invention relates to a novel method and apparatus for performing seamless handoff of a mobile station between radio access networks having different wireless interfaces during wireless packet data service operation.
2. Background
The use of code division multiple access (CDMA) modulation techniques is one of several techniques for facilitating communications in which a large number of system users are present. Other multiple access communication system techniques, such as time division multiple access (TDMA), frequency division multiple access (FDMA) and AM modulation schemes such as amplitude companded single sideband (ACSSB) are known in the art. These techniques have been standardized to facilitate interoperation between equipment manufactured by different companies. Code division multiple access communication systems have been standardized in the United States in Telecommunications Industry Association TIA/EIA/IS-95-B, entitled “MOBILE STATION-BASE STATION COMPATIBILITY STANDARD FOR DUAL-MODE WIDEBAND SPREAD SPECTRUM CELLULAR SYSTEMS”, and referred to herein as IS-95. In addition, a new standard for CDMA communication systems has been proposed in the United States in Telecommunications Industry Association (TIA), entitled “Upper Layer (Layer 3) Signaling Standard for cdma2000 Spread Spectrum Systems, Release A—Addendum 1”, dated Oct. 27, 2000, and referred to herein as “1x.” An additional standard for providing high speed data services has been proposed in the TIA, entitled “cdma2000 High Rate Packet Data Air Interface Specification,” dated Oct. 27, 2000, and referred to herein as “HDR.”
The International Telecommunications Union recently requested the submission of proposed methods for providing high rate data and high-quality speech services over wireless communication channels. A first of these proposals was issued by the Telecommunications Industry Association, entitled “The IS-2000 ITU-R RTT Candidate Submission.” A second of these proposals was issued by the European Telecommunications Standards Institute (ETSI), entitled “The ETSI UMTS Terrestrial Radio Access (UTRA) ITU-R RTT Candidate Submission”, also known as “wideband CDMA” and hereinafter referred to as “W-CDMA.” A third proposal was submitted by U.S. TG 8/1 entitled “The UWC-136 Candidate Submission”, hereinafter referred to as “EDGE.” The contents of these submissions is public record and is well known in the art.
IS-95 was originally optimized for transmission of variable-rate voice frames. Subsequent standards have built on the standard to support a variety of additional non-voice services including packet data services. One such set of packet data services was standardized in the United States in Telecommunications Industry Association TIA/EIA/IS-707-A, entitled “Data Service Options for Spread Spectrum Systems”, incorporated by reference herein, and hereafter referred to as “IS-707.”
IS-707 describes techniques used to provide support for sending Internet Protocol (IP) packets through an IS-95 wireless network. Packets are encapsulated into a featureless byte stream using a protocol called Point-to-Point Protocol (PPP). Using PPP, IP datagrams having lengths of up to 1500 bytes can be transported over a wireless network in segments of arbitrary size. The wireless network maintains PPP state information for the duration of the PPP session, or as long additional bytes may be sent in the continuous byte stream between the PPP end points.
A remote network node such as a personal or laptop computer (PC) connected to a packet-data-capable wireless mobile station (MS) may access the Internet through a wireless network in accordance with the IS-707 standard. Alternatively, the remote network node such as a web browser may be built-in to the MS, making the PC optional. An MS may be any of a number of types of devices including, but not limited to PC card, personal data assistant (PDA), external or internal modem, or wireless phone or terminal. The MS sends data through the wireless network, where it is processed by a packet data serving node (PDSN). The PPP state for a connection between an MS and the wireless network is typically maintained within the PDSN. The PDSN is connected to an IP network such as the Internet, and transports data between the wireless network and other entities and agents connected to the IP network. In this way, the MS can send and receive data to another entity on the IP network through the wireless data connection. The target entity on the IP network is also called a correspondent node.
The MS must obtain an IP address before sending and receiving IP packets over the IP network. In some early implementations, the MS was assigned an IP address from a pool of addresses belonging exclusively to the PDSN. Each PDSN was connected to one or more Radio Access Networks (RANs) associated with a limited geographical area. When the MS moved out of the area served by the first PDSN, data addressed to the MS through the first PDSN could not reach the MS. If the MS moved into an area served by a second PDSN, the MS would have to be assigned a new IP address from the address space of the second PDSN. Any ongoing connection with a correspondent node that was based on the old IP address would be abruptly terminated.
In order to prevent connections from being lost when moving from PDSN to PDSN, MSs use a protocol known as mobile IP. The Internet Engineering Task Force (IETF) has standardized mobile IP in request for comments (RFC) 2002, entitled “IP Mobility Support,” published in October 1996, and well known in the art. The use of mobile IP in cdma2000 networks has been standardized in EIA/TIA/IS-835, entitled “Wireless IP Network Standard,” dated June, 2000, and referred to herein as “IS-835.” In mobile IP, the PDSN does not provide an IP address from its own pool of addresses. Instead, the PDSN acts as a foreign agent (FA) that facilitates assignment of an address from a home agent (HA) located somewhere in the IP network. The MS communicates through the FA to the HA, and receives an IP address assigned from an address pool belonging to the HA. When the MS moves from a first PDSN to a second PDSN, the MS communicates through the second PDSN and FA in order to re-register its existing IP address with the HA.
IS-707 and IS-835 describe a dormant mode, in which a wireless link that was established for transporting packet data, but which is idle for a certain period of time, may be reclaimed by the network without terminating the associated PPP session. When the flow of packet data resumes, the wireless link is re-established without having to repeat PPP configuration and negotiation. Preserving the PPP state when the wireless link has been terminated thus enables the MS and the wireless network to resume sending packet data more quickly than if the PPP state had to be re-established.
The proposed 1x standard provides mechanisms to update routing between an HA and multiple PDSNs and 1x RANs. The proposed HDR standards provide mechanisms to update routing between an HA and multiple PDSNs and HDR RANs. Both the HDR and 1x standards can effectively update packet routing even when an MS changes RANs while in dormant mode, as long as the MS does not move to a RAN using a different type of wireless interface. For example, if an MS moves from a 1x RAN to an HDR RAN while dormant, routing ambiguities or redundancies can occur, and packets can be lost. As these various systems are deployed, there will be a need for mechanisms to effectively update routing of packets to an MS moving between RANs using different types of wireless interfaces.